Swami Vivekananda further elaborates on the theme of what defines a real spiritual Guide, Teacher or Guru ?
"Now in intellectual development we can get much help from books, but in spiritual development, almost nothing.
In studying books, sometimes we are deluded into thinking that we are being spiritually helped; but if we analyse ourselves, we shall find that only our intellect has been helped, and not the spirit. That is the reason why almost everyone of us can speak most wonderfully on spiritual subjects, but when the time of action comes, we find ourselves so woefully deficient. It is because books cannot give us that impulse from outside. To quicken the spirit, that impulse must come from another soul.
That soul from which this impulse comes is called the Guru, the teacher; and the soul to which the impulse is conveyed is called the disciple, the student. In order to convey this impulse, in the first place, the soul from which it comes must possess the power of transmitting it, as it were, to another; and in the second place, the object to which it is transmitted must be fit to receive it.
The seed must be a living seed, and the field must be ready ploughed; and when both these conditions are fulfilled, a wonderful growth of religion takes place. "The speaker of religion must be wonderful, so must the hearer be"; and when both of these are really wonderful, extraordinary, then alone will splendid spiritual growth come, and not otherwise.
These are the real teachers, and there are the real students. Besides these, the others are playing with spirituality — just having a little intellectual struggle, just satisfying a little curiosity — but are standing only on the outward fringe of the horizon of religion"
How are we to know a teacher then? In the first place, the sun requires no torch to make it visible. We do not light a candle to see the sun. When the sun rises, we instinctively become aware of its rising; and when a teacher of men comes to help us, the soul will instinctively know that it has found the truth.
Truth stands on its own evidences; it does not require any other testimony to attest it; it is self-effulgent. It penetrates into the inmost recesses of our nature, and the whole universe stands up and says, "This is Truth." These are the very great teachers, but we can get help from the lesser ones also; and as we ourselves are not always sufficiently intuitive to be certain of our judgment of the man from whom we receive, there ought to be certain tests. There are certain conditions necessary in the taught, and also in the teacher.
In the teacher we must first see that he knows the secret of the scriptures.The whole world reads scriptures — Bibles, Vedas, The Koran and others; but they are only words, external arrangement, syntax, the etymology, the philology, the dry bones of religion. The teacher may be able to find what is the age of any book, but words are only the external forms in which things come. Those who deal too much in words and let the mind run always in the force of words lose the spirit. So the teacher must be able to know the spirit of the scriptures.
The second condition necessary in the teacher is that he must be sinless.The question was once asked me in England by a friend, "Why should we look to the personality of a teacher? For the knowledge that the physical sciences require is simply intellectual and depends on intellectual strength; a man can have in such a case a gigantic intellectual power without the least development of his soul. But in the spiritual sciences it is impossible from first to last that there can be any spiritual light in that soul which is impure. What can such a soul teach? It knows nothing. Spiritual truth is purity. Therefore in the teacher of spirituality, purity is the one thing indispensable; we must see first what he is, and then what he says.
To give a simile: If a heater is hot, it can convey heat vibrations, but if not, it is impossible to do so. Even so is the case with the mental vibrations of the religious teacher which he conveys to the mind of the taught. It is a question of transference, and not of stimulating only our intellectual faculties. Some power, real and tangible, goes out from the teacher and begins to grow in the mind of the taught. Therefore the necessary condition is that the teacher must be true.
The third condition is motive. We should see that he does not teach with any ulterior motive, for name, or fame, or anything else, but simply for love, pure love for you. When spiritual forces are transmitted from the teacher to the taught, they can only be conveyed through the medium of love; there is no other medium that can convey them. Any other motive, such as gain or name, would immediately destroy the conveying medium; therefore all must be done through love. One who has known God can alone be a teacher. When you see that in the teacher these conditions are fulfilled, you are safe; if they are not fulfilled, it is unwise to accept him. There is a great risk, if he cannot convey goodness, of his conveying wickedness sometimes. This must be guarded against; therefore it naturally follows that we cannot be taught by anybody and everybody.